Free radical scavengers can differentially modulate the genotoxicity of amsacrine in normal and cancer cells

Amsacrine is an acridine derivative drug applied in haematological malignancies. It targets topoisomerase II enhancing the formation of a cleavable DNA-enzyme complex and leading to DNA fragmentation in dividing cancer cells. Little is known about other modes of the interaction of amsacrine with DNA, by which it could affect also normal cells. Using the alkaline comet assay, we showed that amsacrine at concentrations from the range 0.01 to 10 microM induced DNA damage in normal human lymphocytes, human promyelocytic leukemia HL-60 cells lacking the p53 gene and murine pro-B lymphoid cells BaF3 expressing BCR/ABL oncogene measured as the increase in percentage tail DNA. The effect was dose-dependent. Treated cells were able to recover within a 120-min incubation. Amifostine at 14 mM decreased the level of DNA damage in normal lymphocytes, had no effect on the HL-60 cells and potentiated the DNA-damaging effect of the drug in BCR/ABL-transformed cells. Vitamin C at 10 and 50 microM diminished the extent of DNA damage in normal lymphocytes, but had no effect in cancer cells. Pre-treatment of the cells with the nitrone spin trap, N-tert-butyl-alpha-phenylnitrone or ebselen, which mimics glutathione peroxidase, reduced the extent of DNA damage evoked by amsacrine in all types of cells. The cells exposed to amsacrine and treated with endonuclease III and 3-methyladenine-DNA glycosylase II, the enzymes recognizing oxidized and alkylated bases, respectively, displayed greater extent of DNA damage than those not treated with these enzymes. The results obtained suggest that free radicals may be involved in the formation of DNA lesions induced by amsacrine. The drug can also methylate DNA bases. Our results indicate that the induction of secondary malignancies should be taken into account as diverse side effects of amsacrine. Amifostine may potentate DNA-damage effect of amsacrine in cancer cells and decrease this effect in normal cells and Vitamin C can be considered as a protective agent against DNA damage in normal cells.     

Interaction of maize (Zea mays) protein phosphatase 2A with tubulin

Immunological and biochemical evidence has been obtained for an interaction of maize protein phosphatase 2A (PP2A) holoenzyme with tubulin. Tubulin co-purifies with maize seedling PP2A. Affinity chromatography of the maize PP2A preparation on immobilized tubulin revealed two peaks of phosphorylase alpha phosphatase activity. In one of the peaks, the catalytic (C) and constant regulatory (A) subunits of PP2A were identified by Western blotting. The subunits (C and A) of PP2A were co-immunoprecipitated from maize seedlings homogenate by an anti-alpha-tubulin antibody. The interaction of plant PP2A with tubulin indicates a possible role of reversible protein phosphorylation in the dynamic structure of plant cytoskeleton.     

PDZ domains - common players in the cell signaling

PDZ domains are ubiquitous protein interaction modules that play a key role in cellular signaling. Their binding specificity involves recognition of the carboxyl-terminus of various proteins, often belonging to receptor and ion channel families. PDZ domains also mediate more complicated molecular networks through PDZ-PDZ interactions, recognition of internal protein sequences or phosphatidylinositol moieties. The domains often form a tandem of multiple copies, but equally often such tandems or single PDZ domain occur in combination with other signaling domains (for example SH3, DH/PH, GUK, LIM, CaMK). Common occurrence of PDZ domains in Metazoans strongly suggests that their evolutionary appearance results from the complication of signaling mechanisms in multicellular organisms. Here, we focus on their structure, specificity and role in signaling pathways.     

Selection of low-molecular-mass trypsin and chymotrypsin inhibitors based on the binding loop of CMTI-III using combinatorial chemistry methods

Using a combinatorial chemistry approach, a decapaptide library containing the N-terminal fragment of trypsin inhibitor CMTI-III was synthesized by the solid-phase method. The peptide library was screened for trypsin and chymotrypsin inhibitory activity applying the iterative method in solution. Two decapeptides were selected and resynthesized for each enzyme. The association equilibrium constants ((1.1+/-0.2)x10(8) and (7.3+/-1.6)x10(7)) determined for peptides with trypsin inhibitory activity indicate that they are 3-4-fold less active than the CMTI inhibitors. On the other hand, they are significantly more effective as compared with the starting sequence. Two peptides selected as chymotrypsin inhibitors displayed about 10 times higher activity (1.7+/-0.4)x10(7) and (1.1+/-0.2)x10(7), respectively) than those monosubstituted in position P(1) of the CMTI-III analogue. Considering low molecular weight of peptides selected and the lack of conformational constraints in their structures, the results are promising. They are good templates as starting sequences for further selection of small, peptidomimetic proteinase inhibitors.     

Selectivity of 4,5,6,7-tetrabromobenzimidazole as an ATP-competitive potent inhibitor of protein kinase CK2 from various sources

Like the previously reported 4,5,6,7-tetrabromobenzotriazole (TBBt), the structurally related 4,5,6,7-tetrabromobenzimidazole (TBBz) is a selective ATP-competitive inhibitor of protein kinase CK2 from such divergent sources as yeast, rat liver, Neurospora crassa and Candida tropicalis, with K(i) values in the range 0.5-1 microM. It is virtually inactive vs. PKA, PKC, and a very weak inhibitor of protein kinase CK1. The corresponding tetrachlorobenzimidazole (TCBz) is a much weaker inhibitor of CK2, like tetrachlorobenzotriazole (TCBt) relative to TBBt. Bearing in mind the similarity of the van der Waals radii of Br (1.95 A) and CH(3) (2.0 A), the corresponding much less hydrophobic 4,5,6,7-tetramethylbenzotriazole (TMeBt) was prepared and found to be a very weak inhibitor of CK2, as well as of CK1. An unexpected, and significant, difference between TBBt and TBBz are their inhibitory activities vs. the yeast protein kinase PK60S, which phosphorylates, both in vitro and in intact yeast cells, three of the five pp13 kDa ribosomal surface acidic proteins in yeast cells. TBBt was previously noted to be a more effective inhibitor of PK60S than of yeast CK2; by contrast, TBBz is a relatively feeble inhibitor of PK60S, hence more selective than TBBt vs. CK2 in yeast cells. TMeBt was virtually inactive vs PK60S. Like TBBt, TBBz is an additional lead compound for development of more potent inhibitors of CK2.     

Administration of a nitric oxide synthase inhibitor counteracts prostaglandin F2-induced luteolysis in cattle

The objective of this study was to determine whether nitric oxide (NO) is produced locally in the bovine corpus luteum (CL) and whether NO mediates prostaglandin F2alpha (PGF2alpha)-induced regression of the bovine CL in vivo. The local production of NO was determined in early I, early II, mid, late, and regressed stages of CL by determining NADPH-d activity and the presence of inducible and endothelial NO synthase immunolabeling. To determine whether inhibition of NO production counteracts the PGF2alpha-induced regression of the CL, saline (10 ml/h; n = 10) or a nonselective NOS inhibitor (Nomega-nitro-l-arginine methyl ester dihydrochloride [L-NAME]; 400 mg/h; n = 9) was infused for 2 h on Day 15 of the estrous cycle into the aorta abdominalis of Holstein/Polish Black and White heifers. After 30 min of infusion, saline or cloprostenol, an analogue of PGF2alpha (aPGF2alpha; 100 microg) was injected into the aorta abdominalis of animals infused with saline or L-NAME. NADPH-diaphorase activity was present in bovine CL, with the highest activity at mid and late luteal stages (P < 0.05). Inducible and endothelial NO synthases were observed with the strongest immunolabeling in the late CL (P < 0.05). Injection of aPGF2alpha increased nitrite/nitrate concentrations (P < 0.01) and inhibited P4 secretion (P < 0.05) in heifers that were infused with saline. Infusion of L-NAME stimulated P4 secretion (P < 0.05) and concomitantly inhibited plasma concentrations of nitrite/nitrate (P < 0.05). Concentrations of P4 in heifers infused with L-NAME and injected with aPGF2alpha were higher (P < 0.05) than in animals injected only with aPGF2alpha. The PGF2alpha analogue shortened the cycle length compared with that of saline (17.5 +/- 0.22 days vs. 21.5 +/- 0.65 days P < 0.05). L-NAME blocked the luteolytic action of the aPGF2alpha (22.6 +/- 1.07 days vs. 17.5 +/- 0.22 days, P < 0.05). These results suggest that NO is produced in the bovine CL. NO inhibits luteal steroidogenesis and it may be one of the components of an autocrine/paracrine luteolytic cascade induced by PGF2alpha.     

Substitution pattern of 3-deoxy-D-manno-oct-2-ulosonic acid in bacterial lipopolysaccharides investigated by methylation analysis of whole LPS

3-Deoxy-D-manno-oct-2-ulosonic acid (Kdo) is a constituent of the inner core part of bacterial lipopolysaccharides (LPS). This sugar may contribute to biological activities of the LPS, the type of substitution of Kdo is thus of importance and this work is aimed at the evaluation of a method for monitoring the substitution of Kdo in LPS. The procedure consists of three steps, namely permethylation of the lipopolysaccharide, with iodomethane and sodium methylsulfinylmethanide or NaOH in Me(2)SO, or with methyl triflate, then the product is methanolysed with HCl in MeOH and acetylated with acetic anhydride in pyridine. The resulting partially methylated acetates of Kdo methyl glycosides were analyzed by gas-liquid chromatography-electron impact ionization mass spectrometry (GLC-MS). For several derivatives of Kdo, specific GLC retention times and MS fragmentation patterns were determined. Lipopolysaccharides from several bacterial strains were isolated and analyzed with three different methods of methylation. The complete solubilization of the LPS in the acid form allows diminishing possible undermethylation. Sodium methylsulfinylmethanide is the most efficient agent in the permethylation of the whole LPS, of all the tested procedures. Methylation with methyl triflate allows the detection of base labile substituents on Kdo residues.     

Androgens and FSH affect androgen receptor and aromatase distribution in the porcine ovary

In the present study the authors investigated whether androgens could interact with FSH to induce aromatase and androgen receptor expression in porcine granulosa cells. Dissected whole porcine follicles (small, medium, and large) were incubated for 8 hours in M199 medium supplemented with testosterone (10(-7) M), FSH (100 ng/ml) or both those hormones. After incubation, the follicles were fixed and immunostained to visualise androgen receptor and aromatase. In cultures of granulosa cells isolated from small and large follicles, oestrogen secretion was measured by appropriate RIA. Incubation of follicles with testosterone and FSH increased aromatase immunoreactivity in preantral and early antral (i.e. small) follicles. The immunostaining for androgen receptor was slightly higher in medium follicles, while such hormonal stimulation had no effect on small and large follicles. Moreover, granulosa cells isolated from small follicles cultured with both testosterone and FSH produced more estradiol than control cultures (40 pg vs. 100 pg/10(5) cells). The level was relatively close to that obtained in the culture of control granulosa cells isolated from large preovulatory follicles (105 pg/10(5) cells). These results indicate that testosterone acts synergistically with FSH to increase aromatase expression in the small porcine follicles.     

Purinergic regulation of glucose and glutamine synthesis in isolated rabbit kidney-cortex tubules

The effects of extracellular purinergic agonists and their breakdown products on glucose and glutamine synthesis in rabbit kidney-cortex tubules incubated with aspartate + glycerol or alanine + glycerol + octanoate were investigated. A rapid extracellular degradation of ATP was accompanied by an accumulation of AMP, inosine, and hypoxanthine. Extracellular ATP and its breakdown products accelerated glucose synthesis in renal tubules, while ammonium released from adenine-containing compounds enhanced glutamine synthesis and diminished the degree of gluconeogenesis stimulation. In contrast to AMP and inosine, ATP evoked calcium signals, while both ATP and inosine decreased intracellular cAMP content and accelerated the flux through fructose-1,6-bisphosphatase as concluded from changes in gluconeogenic intermediates. Since (i) the activity of partially purified renal fructose-1,6-bisphosphatase was increased upon protein phosphatase-1 treatment and decreased following treatment of previously dephosphorylated enzyme with protein kinase A catalytic subunit and (ii) both 8-bromoadenosine 3',5'-cyclic monophosphate and 8-(4-chlorophenyltio)-cAMP inhibited renal glucose synthesis, it seems likely that in rabbit renal tubules ATP and inosine stimulate gluconeogenesis via cAMP decrease, which favors the appearance of a more active, dephosphorylated form of fructose-1,6-bisphosphatase, a key gluconeogenic enzyme.     

Salicylate suppresses macrophage nitric-oxide synthase-2 and cyclo-oxygenase-2 expression by inhibiting CCAAT/enhancer-binding protein-beta binding via a common signaling pathway

We determined whether salicylate at pharmacological concentrations inhibits nitric-oxide synthase-2 (NOS-2) and cyclo-oxygenase-2 (COX-2) expressions in RAW 264.7 stimulated with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma). Cells were treated with sodium salicylate (10(-7)-10(-4) m) or vehicle for 30 min followed by LPS+IFN-gamma for up to 24 h. Salicylate suppressed NOS-2 and COX-2 protein levels and promoter activities stimulated by LPS+IFN-gamma for 4 h in a concentration-dependent manner but had no effect on NOS-2 expression stimulated by the combined agonists for 24 h. Results from promoter analysis indicate that the binding of CCAAT/enhancer-binding protein beta (C/EBPbeta) to its cognate site at -150/-142 on the NOS-2 promoter region was essential for NOS-2 expression at 4 h but not at 24 h. Salicylate reduced C/EBPbeta binding at 4 h and did not alter its binding at 24 h. NOS-2 and COX-2 protein levels and C/EBPbeta binding stimulated by LPS+IFN-gamma for 4 h were inhibited by a similar battery of signaling inhibitors, suggesting a common pathway for NOS-2 and COX-2 expression. Kinetic analysis indicates that NOS-2, similar to COX-2 expression, at 4 h was largely due to the action of LPS, which induced C/EBPbeta binding, whereas its expression at a longer time point was contributed by IFN-gamma. Our findings implicate two distinct pathways for NOS-2 expression induced by LPS+IFN-gamma. Salicylate at pharmacological concentrations is capable of suppressing the early phase of NOS-2 and COX-2 expression by blocking C/EBPbeta binding.